The present invention relates to a streaming delivery method for transmitting media data such as video, audio, etc. through a network and a proxy delivery apparatus for relaying and delivering streaming data.
Streaming delivery is performed for taking video/audio information of movie, live broadcasting, etc. in a computer, compressing and encoding the video/audio information and delivering the video/audio information to an audience terminal.
Generally, in stream delivery, a delivery server apparatus (hereinafter referred to as “server”) managed by a contents provider processes a contents delivery preparation request received from a client terminal apparatus (hereinafter referred to as “client terminal”) such as a PC (Personal Computer) or an STB (Set Top Box) operated by a user and sends necessary information on a media file as a subject of streaming delivery back to the client terminal.
When the server receives a delivery control request from the client terminal, the server reads media data in the media file from a storage device such as a hard disk drive. The server splits (packetizes) the read media data into parts (packets) by a suitable size in accordance with a rule accepted by respective applications of the server and the client terminal to thereby construct packets in accordance with a network protocol and continuously transmits the packets to the client terminal through a network at an appropriate communication rate (bit rate).
In streaming delivery, as a protocol for controlling delivery of the delivery control request, the delivery preparation request, etc., there has been standardized RTSP described by H. Schulzrinne and two others, “Real Time Streaming Protocol (RTSP)”, April 1998, The Internet Engineering Task Force. As a protocol for transmitting media data by packets constructed according to a network protocol, there has been standardized RTP (Real-Time Transport Protocol) described by H. Schulzrinne and three others, “RTP: A Transport Protocol for Real-Time Applications”, January 1996, The Internet Engineering Task Force.
When streaming delivery is performed through a Wide Area Network (hereinafter referred to as “WAN”) represented by the Internet, a proxy apparatus is used for attaining warrant of delivery quality and reduction in server load. The proxy apparatus is disposed between the server and the client terminal and in a position near the client terminal. The proxy apparatus has a local storage device. The proxy apparatus performs a process for streaming delivery of media data in place of the server. Media data delivered by the proxy apparatus is data distributed from the server in advance or a replica of media data taken out from packets according to the network protocol when streaming delivery packets to be delivered from the server to the client terminal are relayed. The media data is stored in the local storage device.
For example, in U.S. Patent Application Publication No. 2002/0176418, there has been disclosed a proxy apparatus in which a replica of media data to be relayed is formed regardless of the network protocol for transmitting the media data so that a part or all of contents delivered from the server can be stored (cached) in the local storage device and delivered in a transmission protocol and a bit rate according to the request from the client terminal (FIGS. 3 and 9).
When streaming delivery is performed, the server needs to process media data in accordance with parameters specific to the media data to be delivered in such a manner that the media data is split into packets according to the network protocol by a suitable size and that the packets are transmitted in accordance with the delivery bit rate. Generally, the parameters specific to the media data are stored as header information of a media file in the form depending on the format of the media file such as MPEG2 (Moving Picture Experts Group layer 2), MPEG4 (Moving Picture Experts Group layer 4) or other commercial media formats. The parameters vary in terms of interpretation, that is, in terms of control necessary for delivery.
For this reason, the server needs different processes according to media formats to be used in streaming delivery. Servers exclusively used according to media formats are required or delivery control application programs exclusively used in streaming delivery and operating on a server are required.
Also in the proxy apparatus described in U.S. Patent Application-Publication No. 2002/0176418, delivery control application programs exclusively used according to media formats to be used are required because the U.S. Patent Application Laid-Open has disclosed that the proxy apparatus performs the same streaming delivery as in the server to the client terminal.
The process for storing a replica of media data in the local storage device while relaying packets in a streaming delivery manner is a process depending on each media format. Accordingly, application programs exclusively used according to media formats must be prepared in the proxy apparatus so that the proxy apparatus can satisfy different media formats. As a result, the cost necessary for updating and managing the proxy apparatus becomes high.
When a large-scale delivery network through a WAN is constructed, a large number of such proxy apparatuses are disposed in a position near the client terminal with respect to the server. Accordingly, in the large-scale delivery network, reduction in the equipment and management cost of the proxy apparatuses necessary for new media formats is a problem to be solved.
Accordingly, a proxy apparatus improved in equipment cost and management cost needs to be put into practice.